1. Field of Invention
This invention relates to an optical communication system and, more particularly, to an optical communication system wherein once channel of a mixed optical beam may be selectively passed, or blocked and replaced by another signal.
2. Description of the Related Art
Optical communications systems encode information onto a light beam at a transmitting location, transmit the light beam through free space or a medium such as an optical fiber, and then decode the information from the light beam at a receiving location. A great deal of information may be encoded onto the light beam due to its high frequency. Additional information may be transmitted by encoding the additional information onto a second light beam having a slightly different wavelength than the first light beam, mixing the two light beams together at the transmitting location (or several different transmitting locations), transmitting the mixed light beam, separating the two light beams at the receiving location (or several different receiving locations), and then decoding the two sets of information from the two light beams. The amount of information that may be transmitted is increased yet further by using additional light beams in a similar manner, with all of the light beams at slightly different wavelengths. Each of the individual light beams is termed an “optical channel”, so that the mixed light beam may be described as having a number of optical channels.
One form of the optical communications system is a point-to-point system, with a single transmitting location and a single receiving location. A more sophisticated version of the optical communications system includes a number of nodes. Some processing of the mixed light beam may be required at each of nodes. That is, it is ordinarily not the case that there is a single input location for all of the optical channels, and a single output location for all of the optical channels. Nor is it the case that an individual optical channel will always be utilized for a single type of information. For example, individual optical channels may be tapped or extracted from the mixed optical beam at one of the nodes, and/or new information may be added to an individual optical channel to replace that being carried on the optical channel up to that point.
Hardware in the form of light-beam processing equipment is required to implement these operations at the nodes. The hardware must be effective to accomplish the required manipulation of the optical beam and should desirably require minimal human technician support at the point of implementation. The present invention fulfills this need for a specific type of nodal function, and further provides related advantages.